Anatomy of a Noise Gate

The five core controls#

• Threshold — the level the signal has to exceed for the gate to open. Set it just above the noise you want to mute.
• Reduction (or range) — how much volume the gate cuts when it's closed. Full reduction is silence; partial reduction lets a little bleed through, which often sounds more natural.
• Attack — how fast the gate opens once the signal crosses the threshold. Fast for percussive material; slower for sustained sounds.
• Hold — the minimum time the gate stays open after triggering. This is what prevents the gate from "chattering" open and shut rapidly on a wobbling signal.
• Release — how slowly the gate closes once the signal drops back below the threshold. Sets the tail.

The advanced controls#

• Hysteresis — gives the threshold a separate "open" and "close" level. If you set the threshold at -15 dB and hysteresis to -5 dB, the gate opens at -15 dB but only closes at -20 dB. Another defence against chatter.
• Sidechain — feeds a different signal into the detector. Useful for triggering one track from another (e.g. a snare gate keyed by the snare's close mic).
• Detector filters — high-pass and low-pass filters on the detection signal (not the audio itself). Tune them so the gate only listens to the part of the spectrum that belongs to the source — e.g. 100 Hz to 300 Hz to isolate a snare's body from kick rumble and cymbal hiss.
• Monitor — temporarily routes the detection signal to the output so you can hear what the gate is listening to. Always switch it off again before printing.
• Gate vs. Ducker — a gate quiets the signal when it's below the threshold; a ducker quiets it when it's above. Duckers are most useful with a sidechain (the classic example: pulling music down when a voiceover speaks).
• Lookahead — lets the gate analyse a few milliseconds ahead so it can open in time for fast transients. Costs a little CPU and latency.
• Open / Close indicator — shows whether the gate is currently letting audio through.